The present invention pertains to an apparatus for positioning lumber pieces for selective end trimming.
In saw milling, the end trimming operation is the final sawing step before stacking lumber for drying. Its purpose is to cut the pieces into commercial lengths as determined by market demand in North America and overseas, while removing defects which would cause quality downgrading and therefore loss in value. In order to achieve the optimum value recovery, the lumber pieces are first scanned along their whole length to locate defects and to allow a computer to determine the cut to be made at each end of the piece by one of an array of saws disposed at a fixed spacing (ordinarily one or two feet) across the width of a lumber trimmer and therefore along the length of the pieces to be trimmed. Between the scanning and trimming sections, a lumber positioning system is provided along the lumber conveyor wherein each lumber piece is moved along its longitudinal axis so as to place its ends at a planned distance from two saws pre-selected by the computer in accordance with the original length of the pieces and the type of defects determined by the scanning means.
A most common method of positioning lumber for end trimming consists at present in placing power driven rolls parallelly to the conveying chains of the lumber conveyor and at a slightly higher elevation, (such as xe2x85x9 of an inch) than that of the chains. Contact of these rolls with the underside of the lumber pieces causes them to move axially, across the chains, until reaching one of several adjustable bumper plates or fences placed side by side, which serve to define a particular cutting position for each piece. The frequency of this individual positioning is up to 2 per second in an average sized sawmill and reaches up to 3 per second in high speed lumber dressing operations for short wood (six to ten feet). In order to complete, within the available time, the necessary axial displacement of up to 2 feet for some pieces, an array of fast rotating 8 foot long rolls is required, plus a number of pneumatically actuated bumper plates disposed side by side along a distance at least equal to the length of the rolls. Sectional lifting skids are also needed between the chains so as to prevent further contact with the rolls for a piece that has reached its planned position within the positioning area.
A system such as described represents over two tons of mechanical equipment, with the necessary power input, a considerable supply of compressed air, plus the mechanical maintenance associated with a high speed operation generating heavy impact loads. Besides such inconveniences, this type of system is marginally accurate as the method of positioning the board by propelling it endwise against a stationary bumper produces a xe2x80x9cbounce backxe2x80x9d effect which varies with the weight of the piece and its acquired speed.
One example of this type of machine may be found described in U.S. Pat. No. 5,142,955 issued Sep. 1, 1992 to Hale.
An object of the present invention is to perform accurate endwise positioning of sawn lumber for the trimming operation; this is achieved by means of an apparatus which is much lighter than the one described above and does not involve high speed travel and abrupt stoppage of the material being positioned.
The lumber positioning apparatus of the present invention therefore comprises:
a frame;
carrying means for lumber positioning gates, mounted on the frame and drivingly associated in synchronism with the conveyor means;
a series of successive lumber positioning gates operatively mounted to the gate carrying means; the gates being spaced at intervals corresponding to the uniform spacing of the lumber pieces of the conveyor means; and
means responsive to scanner data and computer signals for selectively placing a positioning gate in a vertical position to contact an end of a lumber piece traveling on the conveyor means thereby displacing the lumber piece axially as it moves along the conveyor means; the scanner data responsive means further enabling the gate to be removed from the vertical position and thereby from engagement with the lumber piece whereby the lumber piece is no longer pushed axially as it continues to travel along the longitudinal conveyor direction towards the multiple saw trimmer.
In one preferred embodiment, the lumber positioning apparatus of the present invention is composed basically of a pair of parallel chains moving horizontally and joined together by evenly spaced cross bars at one end of which is mounted a pivoting plate, referred to as a xe2x80x9cpositioning gatexe2x80x9d. These chains are installed along one side of a multiple chain transfer which carries lumber pieces transversally and parallel to one another and at an even spacing from one another. The present invention requires that the lumber pieces first be brought to an even end line on one side of the chain transfer, that the spacing of the positioning gates be similar to that of the lumber pieces on the transfer chains, that the speed of the two chain systems be synchronized and that a converging angle be provided between the two chain systems, in their generally common direction of travel. Under these conditions, the position of any gate may be made to coincide at all times with the passage of each piece on the lumber transfer, causing the gate to make contact with and push the corresponding piece axially, as long as such gate is maintained in a vertical position by its actuating mechanism which, in turn, is computer controlled from the scanner data acquired upstream of the system. Whenever, somewhere along the length of the positioning apparatus, a piece has reached its correct position, a signal from the aforesaid computer control system causes the corresponding gate to cease contact by retracting itself to a horizontal position, leaving the piece to continue towards the trimming saws without further longitudinal movement.
In view of the low performance level of presently known systems as previously described, it can be said that a main object of this invention is to increase the accuracy of positioning of sawn lumber for the trimming operation, which has a direct effect on realizing the full potential value of each lumber piece.
In fact, if it is correctly estimated that the use of a scanner/computer combination to determine the optimum trimming pattern can increase the final product value by some 7% as compared to a visual/manual method, it is no less logical to think that the accuracy in actually locating the pieces with regard to the saws can be responsible for an important part of this gain.
Another object of the present invention is the reduction in size and weight of the necessary mechanical means to effect the positioning of the lumber, as well as the required floor space and power input.
Yet, a further object is to eliminate the high velocity movement of the individual pieces of lumber, terminating in a destructive impact upon reaching the locating bumper, thus at times causing sudden breakdowns of components with resulting losses of production.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that this detailed description, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.